Mechanical stoker and grate elements therefor



United States Patent MECHANICAL STOKER AND GRATE ELEMENTS THEREFOR Johannes Josef Martin, Munich, Germany Application September 28, 1949, Serial No. 118,416 Claims priority, application Germany October 1, 1948 Claims- (Cl. 110-38) The present invention relates to the construction of mechanical stokers in which the fuel bed is agitated by.

grate elements pushing substantially in the direction of the flow of the fuel as well as to stokers in which the fuel bed is inclined and agitated by grate elements pushing substantially in a direction opposite to that of the main movement of the fuel, and to the construction of grate elements for stokers of the type set forth.

It is an object of the present invention to provide a construction and arrangement of the grate elements in a stoker in which rows of the elements form steps extending transversely to the longitudinal axis of the grate and, normally, push the fuel in a direction from the hoppers at the front of the furnace toward the rear of the furnace and in which the elements are moved reciprocatingly and are so constructed and arranged as to return toward the front of the furnace, upon their return or idle stroke, portions of the fuel which are essential for igniting incoming fuel.

It is a further object of the invention to provide a construction and arrangement of the grate elements in a stoker in which the elements normally push the fuel toward the front end of the furnace and in which the individual elements are so constructed and arranged as to selectively return certain fuel particles toward the front of the furnace and promote movement of other particles toward the rear of the furnace.

Both aforesaid objects are achieved by providing a novel configuration of the heads of the individual elements. This new configuration has the additional effect of progressively comminuting, i. e. breaking up or crushing, the pieces of coke and slag formed during combustion and of increasing the combustion efliciency.

According to the invention, at least a part of the reciprocating elements forming a stoking grate are provided with protuberances at their stoking heads which protuberances are of such configuration that they do not interfere with the advance of the fuel by the pushing movement of the elements but impart an additional movement to the fuel when the elements are returned to be readied for the next push, i. e. when they make an idle stroke in the conventional grate. The result is improved maintenance of ignition and combustion in stokers in which the elements push in the direction of the main movement of the fuel, and selective separation of burnt out pieces of fuel and promotion of their movement toward the rear of the furnace in grates where the active stroke of the grate elements is directed against the main movement of the coal; in both cases the construction and arrangement according to the invention causes comminution of fuel lumps larger than a predetermined size.

Further and other objects of the present invention will be hereinafter set forth in the accompanying specification and claims and shown in the drawings, which by Way of illustration show what I now consider to be preferred embodiments of the invention.

In the drawings:

Fig. l is a diagrammatic longitudinal sectional view of a portion of a mechanical stoker in which the fuel is pushed toward the rear of the furnace, improved according to the invention;

Fig. 2 is a diagrammatic top view of a portion of the stoker shown in Fig. 1;

Fig. 3 is a diagrammatic longitudinal sectional view of a portion of a mechanical stoker in which the fuel is pushed by the grate elements toward the front of the furnace, improved according to the invention;

Fig. 4 is a diagrammatic top view of a portion of the stoker illustrated in Fig. 3;

Fig. 5 is a diagrammatic side view of a portion of a pair of grate elements according to the invention;

Fig. 6 is a top view of the portion of the grate elements shown in Fig. 5;

Fig. 7 is a side view of a portion of a modified grate element according to the invention;

Fig. 8 is a top view of the element shown in Fig. 7;

Fig. 9 is a side view of a further modification of a grate element according to the invention;

Fig. 10 is a sectional view of the pusher head of a grate element according to the invention;

Fig. 11 is a sectional view of a modified pusher head of a grate element according to the invention, the section being taken along line XIXI of Figs. 7 and 9.

Like parts are designated by like numerals in all figures of the drawing.

Referring more particularly to Figures 1 and 2 of the drawing, numeral 1 designates grate elements arranged in rows forming steps and being reciprocatingly moved. The top surfaces 8 of some of the elements are provided with protuberances 2 which project rearwards from the head and toward the front of the furnace and have a substantially vertical surface extending substantially transversely to the longitudinal axis of the elements and facing the incoming fuel. The bottom surfaces 10 of the heads of the elements of one row slide on the top surfaces 8 of the grate elements of an adjacent row. Figure 2 shows a preferred arrangement of the elements provided with a protuberance among conventional elements having no protuberance. The first two rows consist of elements all having protuberances. In the next two rows alternate elements have a protuberance and the elements with the protuberance are staggered with respect to the plane elements. The last rows consist of plane elements only. The distribution of the elements with protuberances may be arranged differently without departing from the scope of the invention, for example a plurality of plane elements may be interposed between elements with protuberances, in the same row. The surfaces of the protuberances facing the front of the furnace push particularly the smaller pieces of the coal toward the front of the furnace whenever the elements execute an otherwise relatively ineffective or idle stroke. This effects better maintenance of the base fire and causes return of igniting centers from the main combustion zone toward the front of the furnace after each stoking or active stroke of the elements whereby ignition and combustion are improved. The beneficial effect of the protuberances may be improved or varied by proper choice of the number and relative placement of the elements with and without protuberances.

In inclined grates where the individual elements push the coal back toward the front of the furnace, as illustrated in Figures 3 and 4 and return of burning pieces toward the front is accomplished by the normal action of the elements, improvement of agitation of the fuel bed toward the rear of the furnace is desired in order to make removal of combustion residues more continuous and even. This is accomplished by the present invention by providing the rear of the active heads of some of the elements with protuberances having a substantially vertical surface facing the rear of the furnace and placing such elements in increasing numbers in the rear portion of the grate, for example as shown in Fig. 4, where the last three rows consist of elements with protuberances only, and such elements are interspersed between plane elements in decreasing numbers toward the front of the furnace. The distribution of the new elements among the plane elements may be made in checkered or any other fashion to obtain the desired effect with different kinds of coals. The effect depends on the number of new elements and is caused in this embodiment of the invention also during the normally ineffective or idle stroke of the elements.

The arrangement according to the invention effects a selective removal of combustion residues. Due to fusing with others, pieces of slag become greater the longer the piece is in the fuel bed, and the probability of becoming engaged with a ram or grate element provided with a protuberance increases accordingly. The larger pieces of slag which are more fully burned out are therefore transported toward the rear of the furnace at a greater than average speed. incompletely burned pieces of fuel are smaller and are likely to remain between grate elements with protuberances and to be agitated by conventional grate elements only, i. e. they are merely turned over for promoting combustion and not crushed and pushed toward the ash pit. When the combustion of these small pieces is further advanced, they fuse together with other pieces of like status to a size which can be caught by the protuberances according to the invention and the completely burnt out pieces will be forced toward the ash pit. By providing a suitable number and arrangement of elements with protuberances in a grate, it may be adapted to burn various kinds of fuel and the heat liberated per unit of time and grate surface is considerably increased.

The work of conventional grates of the type referred to supra is substantially limited to overcoming the resistance of fuel to its movement in the desired direction, and such grates have no considerable breaking effect on the fuel pieces. The result is incomplete combustion, particularly of coal containing a high percentage of noncombustibles and/or having a great tendency to coke. If the grates are improved according to the invention, the fuel is not only agitated but its individual pieces are also continuously broken up. This is accomplished by forming the protuberances 4 whose extension a in the direction of the reciprocating motion of the grate elements amounts only to a fraction of the height b of a stoker step, and by forming the pushing head of the adjacent element in such a way that a gap is formed between a protuberance 4 and the pushing head 5 of the adjacent element, which gap receives fuel and crushes it upon opposite reciprocating movement of the adjacent elements. This construction is illustrated in Figures 5 and 6. The rear surfaces 7 of the protuberances 4 are either vertical as in Fig. 5 or rearwardly overhanging like the surfaces 7 of protuberances 4" in Fig. 9 for facilitating catching of the fuel pieces in the gaps between the protuberances 4 or 4" and the heads 5 or 5" of elements of adjacent grate steps. The rear surfaces 7, 7', 7 of the protuberances may be so located on the grate elements as to act in the direction of the main movement of the fuel bed as in Fig. 3 or in the opposite direction as in Fig. l. The same grate may be provided with elements of both types, i. e. having vertical and overhanging rear surfaces. The forward surfaces of the protuberances 4. 4', and 4" are designated by numerals 9, 9', and 9", respectively.

The head surfaces 5' of the elements 1', which are provided with protuberances 4', may be placed at a right angle to the longitudinal axis of the elements, as shown in Figures 7 and 8, or they may be arranged at an oblique angle to the longitudinal axis as the surface 5" of element 1" shown in Figure 9. In the modification illustrated in Figs. 5 and 6, the head surfaces 5 of the elements 6 facing the rear surfaces 7 of the protuberances 4 of adjacent elements 1 are also at a right angle to the longitudinal axes of the elements and also to the surface 8 of the elements which slidingly support an adjacent element.

The cross section of the head portion of the elements provided with protuberances may be either rectangular as shown in Figure 10 or trapezoidal as shown in Figures 5 to 9 and 11.

While I believe the above described embodiments of my invention to be preferred embodiments, I wish it to be understood that I do not desire to be limited to the exact details of method, design and construction shown and described, for obvious modifications will occur to a person skilled in the art, for example the cooperating elements of two successive rows or steps of the grate may be arranged in staggered relation instead of in line as shown in Figures 2 and 4.

I claim:

1. A stoker grate comprising a plurality of longitudinal inclined grate elements placed longitudinally of the grate,

said elements forming rows transversely of the grate and being reciprocatingly operated in the direction of the inclined longitudinal axis of the elements, each element having a head portion extending into the fuel and having a bottom and a top surface substantially parallel to the inclined longitudinal axis of the element, the bottom surfaces of the elements of one row sliding on the top surfaces of the elements of an adjacent row, a protuberance extending from the top surfaces of the head portions of at least a part of said elements, said protuberances having a first surface portion extending substantially parallel to the general direction of the movement of the fuel toward the rear of the grate, said head portion having an end surface, said protuberance having a second surface portion extending substantially at a right angle to the general direction of the movement of the fuel and facing toward the rear of the grate and facing the end surface of the head portion of a grate element of an adjacent row and forming a gap therewith for receiving and crushing pieces of fuel upon relative movement of the elements.

2. In a stoker grate as set forth in claim 1, the number of elements provided with a protuberance being greater in the rows at the front of the grate than in the following rows.

3. In a stoker grate as set forth in claim 1, the number of elements provided with a protuberance increasing in the rows toward the rear of the grate.

4. In a stoker grate as set forth in claim 1, the elements with a protuberance and the elements without a protuberance being placed in substantially checkered fashion relative to one another in a portion of the grate.

5. In a stoker grate as set forth in claim 1, the section of said protuberances taken in a plane substantially transverse to the longitudinal axis of the elements being substantially rectangular.

6. In a stoker grate as set forth in claim 1, the section of said protuberances taken in a plane substantially transverse to the longitudinal axis of the elements being substantially trapezoidal.

7. In a stoker grate as set forth in claim 1, the number of elements provided with a protuberance being greater in the rows at one end of the grate than in the middle of the grate.

8. A stoker grate as defined in claim 1, said second surface portion being substantially vertical.

9. A stoker grate as set forth in claim 1, the number of elements provided with a protuberance being different in different rows.

10. In a stoker grate of the type having a plurality of reciprocatingly operated steps composed of a plurality of juxtapositioned grate elements, each element having a head portion contacting the fuel, a protuberance extending rearward from the head portions of at least a part of said grate elements and effecting movement of the fuel at the idle stroke of the grate elements in a direction opposite to that produced by the active stroke of the elements said protuberances having a rear surface extending substantially transversely to the longitudinal axis of the grate element and being inclined toward the vertical axis so as to overhang toward the rear of the element.

References Cited in the file of this patent UNITED STATES PATENTS 206,033 Miller July 16, 1878 367,376 Dolliver Aug. 2, 1887 1,223,830 Reagan Apr. 24, 1917 1,908,992 Martin May 16, 1933 2,431,799 Gaffney Dec. 2, 1947 FOREIGN PATENTS 14,609 Great Britain 1912 52,301 Australia Feb. 26, 1912 348,904 Great Britain May 21, 1931 369,734 Great Britain Mar. 31, 1932 568,164 Germany Jan. 16, 1933 101,940 Australia Sept. 9, 1937 

